Two long-term prescribed fire studies were established near Flagstaff, Arizona in 1976 and 1977. One of the sites, Chimney Spring, is located on a basalt soil type and had not received any natural fires for the previous 100 years. The other site, called Limestone Flats, located on a sedimentary soil type, has a similar fire-free period but received a sanitation cut to remove the dead overstory in the early 1960s. The study was designed to test 1-, 2-, 4-, 6-, 8-, and 10-yr burning rotations in southwestern old growth ponderosa pine stands. The primary objective was to determine if a particular burning rotation would reduce and maintain the natural accumulation of fuels and reduce the stand density to a condition that would withstand a wildfire under average worst conditions. Permanent photo points were initiated at the time each study area was established, and they have been retaken periodically. Visual changes in stand structure correspond to the reduction in number of stems but don't reflect the continuation or increase in basal area per acre. The photos also show the initial reduction in large woody fuels followed by their incremental return.